Quick opening device for dry-pipe valves of automatic sprinkler systems

ABSTRACT

A component for automatic sprinkler systems employed for fire protection is provided which is useful in dry-pipe systems to cause rapid opening of the dry-pipe valve of such systems in response to a slight but rapid decrease of air pressure in the sprinkler piping network attendant upon opening of a sprinkler head. Slow decreases in such pressure in relation to atmospheric pressure are off-set by an atmospheric bleed valve, a readily accessible adjustment for altering and visibly indicating the trip-off pressure is provided, and provision is made for either electrical or pneumatic operation.

United States Patent 1191 Willms 1451 Apr. 17, 1973 [54] QUICK OPENING DEVICE FOR I)RY-. PIPE VALVES-OF AUTOMATIC SPRINKLER SYSTEMS [75] Inventor: Charles F. Willms, Rutherford, NJ.

[73] Assignee: Norris Industries, Inc., Los Angeles,

Calif.

[22] Filed: July 15, 1971 21 App1.No.: 162,958 I Related (1.8. Application Data 7 [62] Division of Ser. No. 863,985, Oct. 6, 1969, Pat. No.

52 U.S.Cl ..251/s7,251/25, 137/010. 8,

s I e 1 169/19 511 1m. c1. ..'A62c 37/06,Fl6k 31/145 581 Field of Search ..l37/460, 557, 010. 8;

[56] References Cited UNITED STATES PATENTS 1,153,850 .9/1915 Meier ..l37/46O FORElGN PATENTS OR APPLICATIONS 1,159,003 12/1963 Germany ,251/57 Primary ExaminerArnold Rosenthal Attorneyl-luebner & Worrel ABSTRACT A component for automatic sprinkler systems employed for fire protection is provided which is useful in dry-pipe systems to cause rapid opening of the drypipe valve of such systems'in response to a slight but rapid decrease of air pressure in the sprinkler piping network attendant upon opening of a sprinkler head. Slow decreases in such pressure in relation to atmospheric pressure are off-set by an atmospheric bleed valve, a readily accessible adjustment for altering and visibly indicating the trip-off pressure is provided, and provision is made for either electrical or pneumatic operation.

1 Claim, 5 Drawing Figures TO WATER M0701? WATER SUPPLY PATENTEDAPR 3.727. 878

SHEET 1 [IF 2 66 TO WATER AIR SIDE OF JYSTEM 32 5 *wmzrz SUPPLY H2 J'wvavrag, 61/224155 E W/ZLMS QUICK OPENING DEVICE FOR DRY-PIPE VALVES OF AUTOMATIC SPRINKLER SYSTEMS CROSS-REFERENCE TO RELATED APPLICATION The present application is a division of application Ser. No. 863,985 filed Oct. 6, 1969, now US. Pat. No. 3,616,860, for a Quick Opening Device for Dry-pipe Valves of Automatic Sprinkler Systems.

BACKGROUND F THE INVENTION 1'. Field of the Invention Automatic sprinkler systems embody a network of overhead piping extending throughout a building or area and provided at spaced intervals with sprinkler heads, which are essentially heat-responsive valves which open under the influence of a local conflagration to discharge water from the piping over the area covered by the opened sprinkler or sprinklers.

In locations in which there is no exposure of the piping ofv such systems to freezing temperatures, a wetpipe system may be installed.'ln such a system, water is held in the piping throughout the system, and immediately discharged whenever a sprinkler head opens.

However, in locations in which the piping is likely to be exposed to freezing temperatures, a dry-pipe system must'be installed. In such a system, air is held in the piping'throughout the network of piping. A main control valve, known as a'dry-pipe valve, which is located in an area not exposed to freezing temperatures, opens in response to a ,drop in air pressure in the piping network occasioned by the opening of a sprinkler head, allowing water to flow into the piping network and discharge through the open sprinkler head or heads.

The interval between the opening of a sprinkler head of such a dry-pipe system and the discharge of water from it'necessarily lengthens as the size of the system increases, because the rate at which air can be discharged through an open sprinkler head is limited and the relationship of the volume of air so discharged to the total volume of air in the piping network becomes smaller as that total volume increases.

Among the standards agreed upon for automatic sprinkler systems is one fixing a limit on the interval between the opening of a sprinkler head and the discharge of water from it; it being required to be short enough to afford a reasonable assurance that a tire will not intensify or spread beyond control. In order to comply with this interval standard, it has been necessary in large dry-pipe systems, to provide devices for causing the dry-pipe valve to open in response to the opening of a sprinkler head, at an earlierpoint in time than it would in the absence thereof. Such devices are known as quick-opening devices, exhausters, or ac- 1 v celerators, and it is to the im 'rovernent of this class of comprises an intermediate chamber disposed between an-inlet chamber connected to the water main and an outlet chamber connected to the sprinkler piping network; a normally closed valve being disposed between the inlet and outlet chambers. This valve is prevented from opening as long as the pressure of the air in the sprinkler piping network, which is in excess of the atmospheric pressure, exceeds a predetermined magnitude. Even in the absence of any quick-opening device, the water supply pressure will cause the valve to open if the pressure of the air in the sprinkler piping network falls below a critical point.

Various types of devices have been provided for expediting the opening of such dry-pipe valves upon a decrease in the air pressure in the sprinkler piping network to a predetermined point higher than the point at which such opening would occur were such a device not provided. One type of such device responds to a decrease in pressure in the sprinkler piping network to exhaust air therefrom into the intermediate chamber of the dry-pipe valve, thus rapidly equalizing the pressure above and below a diaphragm forming a part of the valve between the inlet and outlet chambers and permitting the water pressure to open the valve.

Such devices must, however, be capable of discriminating between rapid pressure drops in the sprinkler piping network resulting from opening of a sprinkler head and requiring prompt opening of the dry-pipe valve, and slow pressure drops resulting from lowering of air temperature in the piping network, etc., which must not be allowed to cause opening of the dry-pipe valve. For this reason, prior devices of this type have included dual internal chambers communicating through a restricted orifice; one such chamber being connected to the sprinkler piping network, and the arrangement being such that the device operates only when the pressure in the latter chamber falls below the pressure in the other chamber by a predetermined amount due to inability of the restricted orifice to effect sufficiently rapid equalization.

The restricted orifices of such devices are subject to clogging, allowing them to cause opening of the drypipe valve in response to even slow drops in the pressure of the air in the sprinkler piping network which, of course, is highly undesirable. Furthermore, the point at which such devices will cause opening of the dry-pipe valve can be changed only by adjustment of the restricted orifice.

SUMMARY OF THE INVENTION In contrast to the prior devices referred to above, which rely upon sensing of differences between the ambient pressure in a secondary chamber communicating unrestrictedly with the piping network and the pressure retained in a primary chamber communicating with the piping network through a restricted orifice to cause opening of the dry-pipe valve, the device of the present invention senses differences between the ambient pressure in a secondary chamber communicating unrestrictedly with the piping network and the pressure in a primary chamber communicating through a restricted orifree with the atmosphere instead of with the secondary chamber; the restricted orifice being provided so that slow decreases in pressure in the piping network may be offset by the flow of air through the restricted orifice, while rapid decreases in pressure in the piping system will produce a partial vacuum in the primary chamber the volume of which varies inversely with respect to that of the secondary chamber.

This makes it possible to dispose the restricted orifice between the interior and exterior of the device instead of between two chambers within the device, thus reducing the likelihood of clogging of the orifice and rendering it more easily accessible for cleaning or replacement in the event such clogging should occur.

The primary chamber may be connected directly to a conventional vacuum responsive electrical switch adapted for connection to a solenoid valve so that, upon the occurrence of a partial vacuum in the primary chamber, the solenoid valve will open and admit fluid under pressure to the split seat of the dry-pipe valve of a dry-pipe sprinkler system, thus causing the dry-pipe valve to open and admit water under pressure to the sprinkler pipe net-work much sooner than it would open in response to an air pressure drop in that network.

Alternatively, the primary chamber may be connected to a pilot valve operating mechanism so that, upon the occurrence of a partial vacuum in the primary chamber, a valve will be opened to admit fluid under pressure to the split seat of such a dry-pipe valve to produce the same result.

The point at which the device of the present invention will cause opening of the dry-pipe valve may readily be altered without changing the rate of flow of air through the restricted orifice, and that point is visibly indicated by a scale exteriorly of the device. Such adjustment is effected by varying the compression of a spring counterbalancing the air pressure in the sprinkler piping network.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view partially in section of an embodiment of the present invention designed for electrical control of the dry-pipe valve of an automatic sprinkler system, illustrating diagrammatically the connection of the device to such a system;

FIG. 2 is a detail sectional view taken on the line 2- 2 of FIG. 1, showing the construction of the device supplying the restricted orifice;

FIG. 3 is a circuit diagram showing the electrical connections between the device of the present invention and a solenoid valve for controlling the dry-pipe valve;

FIG. 4 is an illustration, partly in section, of an embodiment of the present invention designed for fluid pressure operation, illustrating diagrammatically the connection between such a device and a dry-pipe automatic sprinkler system; and

FIG. 5 is a detail sectional view taken on the line 5- 5 of FIG. 4, showing a detail of the structure of the device of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS although certain of the other types of dry-pipe valves il- I lustrated in the Fire Protection Handbook" referred to above may be substituted therefor. The valve 10 has its inlet side connected by a pipe 12 to a water supply main 14 through a manually operable valve 16 and its outlet side connected by a pipe 18 to the piping network of a conventional automatic sprinkling system 20 which, when the valve 10 is closed, conventionally is filled with air under higher than atmospheric pressure.

The valve 10, as shown in the U. S. Pat. of Rowley No. 2,667,934 referred to above, comprises a clapper structure Within which is a chamber designated by the reference numeral 53 in said patent, which is known as the split seat" of the dry-pipe valve and which is normally in communication with the atmosphere through a pipe 22 and a drain clapper valve 24 corresponding to the drain clapper valve designated 93 in said patent; this arrangement being such that when fluid under pressure is admitted to the pipe 22, it will effect automatic closure of the drain clapper valve 24 and cause fluid to pass under pressure into the dry-pipe valves split seat" which is the clapper valve chamber designated 53 in said patent, thus causing quick opening of the dry pipe valve 10.

A pipe 25 connects the pipe 22 with a water motor operating an alarm for signalling the opening of the dry-pipe valve 10 and a pipe 26 connects the pipe 25 with the inlet pipe 12 through a manually operable valve 28 which may be opened at any time to test the operability of the alarm.

The elements thus far described in detail are conventional elements of dry-pipe automatic sprinkler systems and form no part of the present invention.

The present invention provides, for incorporation into such a system, a device which is responsive to a slight but rapid decrease of air pressure in the sprinkler piping network, such as the pressure decrease attendant upon opening of a sprinkler head, to cause an immediate admission of fluid into the pipe 22 and consequent rapid opening of the dry-pipe valve 10.

The form of the device of the present invention illustrated in FIGS. 1 to 3, which is designed for electrical operation, comprises a cylindrical body formed by an upper member 30 and a lower member 32 secured together by bolts 34 passing through flanges 36 and 38 on the upper and lower cylindrical members respectively. The upper and lower members 30 and 32 are provided with internal cylindrical cavities defining a compartment 37 which is divided into primary and secondary chambers 39 and 40 by piston means comprising a flexible diaphragm 42 the edge of which is retained between the flanges 36 and 38, and a piston 44 to which the diaphragm 42 is centrally secured by a disk 46 and bolt 48.

The piston means 42, 44 is movable longitudinally within the compartment 37 to inversely vary the relative volumes of the chambers 39 and 40, that is, to increase the volume of the primary chamber 39 as the volume of the secondary chamber 40 is decreased, and vice versa, by means comprising a piston rod 50 extending through a cylindrical opening 52 in the upper member 30 and provided with an O-ring 54 which maintains an hermetic seal between the piston rod 50 and the member 30. A cylindrical spring housing 56 is secured to the upper member 30 by bolts 58, and secured to theupper end of the piston rod 50 is a spring seat 60 guided for longitudinal movement within ,the housing 56 by a pin 62 extending from the seat 60 into a slot 64 in the housing 56. A spring 66 is compressed between the spring seat 60 and an upper spring seat 68 which, likewise, is guided for longitudinal movement within the housing 56 by a pin 70 extending from the upper spring seat 68 into the slot 64.

Means are provided for adjusting the compression of the spring 66 by moving the upper spring seat 68 between the position in which it is shown in full lines and the position in which it is shown in dotted lines. This means comprises a threaded rod 72 the threads of which mate with internal threads in a central aperture 73 in the upper spring seat 68 and the opposite end of which is rotatably mounted in an end closure 74 secured to an end of the housing 56 by pins 76. The outside end of the threaded rod 72 is provided with a non-circular recess 78 into which a mating tool may be inserted to rotate the rod 72 in one direction or the other to alter the compression of the spring 66, and a protective cap 80 is frictionally fitted over the end of the housing 56.

The lower chamber 40 is provided with an opening 82 which is threaded for connection to a pipe 84 extending from the pipe 18 connected to the piping network of the automatic sprinkler system, and a gauge 86 preferably is connected to the pipe 84 for indicating the ambient pressure in the piping network and the chamber 40 which, as previously mentioned, is conventionally maintained above atmospheric pressure. The compression adjustment of the spring 66 is adjusted so that it approximately balances this pressure and thus maintains the piston means 42, 44 at a position intermediate between its extreme positions within the compartment 37.

The chamber 39 normally is maintained at atmospheric pressure; a restricted orifice between it and the atmosphere being provided to restore the pressure therein to atmospheric pressure in the event that relatively slow changes in the air pressure in the network-of sprinkler piping, such as, for instance, pressure changes arising from slowly rising or falling temperatures, cause movement of the piston means 42, 44 in either direction. Such a restricted orifice is provided by a compensating vent fitting 90 threaded upon a sleeve 92 which in turn is threaded into the enlarged upper end of a passage 94 communicating with the chamber 39. This compensating vent fitting, as shown in detail in FIG. 2, may be, for example, a conventional component such as is manufactured by Automatic Sprinkler Corpora tion of America for use in thermo-pneumatic systems, and in this form comprises essentially a hollow body member 94 within which a small mass of kapok 96 may be compressed between disks 97 and 98 by adjustment of a threaded sleeve 99. Such vents are calibrated in the factory by compressing the kapok in the vent'body by screwing down the threaded sleeve 99; the rating being stamped on the vent at the time of calibration and not usually altered thereafter. The interior of the compensating vent fitting communicates at one end with the opening 94 into chamber 39 and atthe other end, through an aperture 101), with the atmosphere.

Means are provided'for actuating an electrical switch whenever the pressure iri the chamber 39 falls below atmospheric pressure by a predetermined amount in response to a drop in the pressure in chamber 40 more rapid than can be offset by the induction of air from the atmosphere through the restricted orifice means comprising the compensating vent fitting 90. This means comprises a threaded opening 102 through the wall of the member 30 into the chamber 39 into which opening is threaded one end of a pipe fitting 104 communicating with a bellows assembly 106 contractible in response to a drop in pressure in the chamber 39 to cause closure of an electrical switch 108 of conventional construction.

Means are provided for automatically admitting fluid pressure to the pipe 22 to cause opening of the dry-pipe valve immediately upon the closing of the switch 108. As shown in FIG. 3, closure of switch 108 completes the circuit from a source of electrical power 110 to a solenoid 1 12 which, when thus energized, opens a valve 114. The valve 114 is disposed in a pipe 116 communicating with a source of fluid pressure such as, preferably, the water pressure supplied through the pipe 12 to the inlet side of the dry-pipe valve 10, although the air pressure in the sprinkler piping network of the automatic sprinkler system may be utilized as such a source of fluid pressure or an entirely independent source of fluid pressure could be employed.

In the operation of the device of the present invention, slow changes in the air pressure in the sprinkler piping network of the automatic sprinkler system are offset by the induction or expulsion of air from the chamber 39 through the compensating vent fitting 90 without effecting closure of the switch 108. However, in the event of a rapid drop of air pressure in the sprinkler piping network, such as the pressure drop produced by the opening of a thermally responsive valve of a sprinkler head, the pressure in the chamber 40 drops rapidly and the piston means 42, 44 moves downwardly, producing a vacuum in the chamber 39 too rapidly to permit it to be offset by the induction of air through the compensating vent 90. The production of a vacuum in the chamber 39 in this manner contracts the bellows assembly 106 causing a closure of the electrical switch 108, energization of the solenoid 112 and opening of the valve 114, admitting fluid pressure through the pipe 116 to a pipe 22. The drain clapper valve 24 closes automatically, as described in the U.S.

Pat. of Rowley No. 2,667,934, and the fluid pressure thereby created in the pipe 22 enters the chamber designated 53 in said patent, causing immediate opening of the dry-pipe valve 10.

The form of the device of the present invention illustrated in FIGS. 4 and 5, which is designed for exclusively fluid pressure operation without electrical elements, comprises a cylindrical body formed by an upper member and a lower member 132 secured together by bolts 134 passing through flanges 136 and 138 on the upper and lower cylindrical members respectively. The upper and lower members 130 and 132 are provided with internal cylindrical cavities defining a compartment 137 which is divided into primary and secondary chambers 139 and 140 by piston means comprising a flexible diaphragm 142 the edge of which is retained between the flanges 136 and 138, and a piston 144.

The piston means 142, 144 is movable longitudinally within the compartment 137 to inversely vary the relative volumes of the chambers 139 and 140; that is, to increase the volume of the primary chamber 139 as the volume of the secondary chamber 140 is decreased, and vice versa, by means comprising a piston rod 150 extending through a cylindrical opening 152 in the upper member 130 and provided with an -ring 154 which maintains an hermetic seal between the piston rod 150 and the member 130. A cylindrical spring housing 156 is secured to the upper member 130 by screws 158, and in engagement with the upper end of the piston rod 150 is a spring seat 160 guided for longitudinal movement within the housing 156 by a pin 162 extending from the seat 160 into a slot 164 in the housing 156. A spring 166 is compressed between the spring seat 160 and an upper spring seat 168 which, likewise, is guided for longitudinal movement within the housing 156 by a pin 170 extending from the upper spring seat 168 into the slot 164.

Means are provided for adjusting the compression of the spring 166 by moving the upper spring seat 168 between the position in which it is shown in full lines and the position in which it is shown in dotted lines. This means comprises a threaded rod 172 the threads of which mate with internal threads in a central aperture 173 in the upper spring seat 168 and the opposite end of which is devoid of threads and is rotatably mounted in an end closure 174 secured to an end of the housing 156 by pins 176. The outside end of the threaded rod 172 is provided with a non-circular recess 178 into which a mating tool may be inserted to rotate the rod 172 in one direction or the other to alter the compression of the spring 166. A protective cap 180 is frictionally fitted over the end of the housing 156.

The secondary chamber 140 is provided with an opening 182 which is threaded for connection to a pipe 184 extending from the pipe 18 connected to the piping network of the automatic sprinkler system, and a gauge 186 preferably is connected to the pipe 184 for indicating the ambient pressure in the piping network and the secondary chamber 140 which, as previously mentioned, is conventionally maintained above atmospheric pressure. The compression adjustment of the spring 166 is adjusted so that it approximately balances this pressure and thus maintains the piston means 142, 144 at a position intermediate between its extreme positions within the compartment 137.

The primary chamber 139 is normally maintained at atmospheric pressure communicating with the atmosphere through a restricted orifice, so that the pressure therein is restored to atmospheric pressure in the event that relatively slow changes in the air pressure in the network of a sprinkler piping, such as, for instance, pressure changes arising from slowly rising or falling temperatures, cause movement of the piston means 142, 144 in either direction.

In the embodiment of the invention shown in FIG. 4, such a restricted orifice is provided by a compensating vent fitting 90 shown in detail in FIG. 2 and described in connection with the embodiment illustrated in FIGS. 1 to 3, this fitting, in the embodiment illustrated in FIG. 4, being threaded onto an externally threaded sleeve 191 which is in turn threaded into an opening 193 in a member 195 defining a cavity 197 communicating with the primary chamber 139 via a tube 199 the ends of which are threaded into openings in the primary chamber 139 and the wall of the cavity 197, respectively.

Means are provided for actuating a valve to permit fluid under pressure to pass from a source of fluid pressure to the split seat of the dry pipe valve 10 whenever the pressure in the primary chamber 139 falls below atmospheric pressure by a predetermined amount in response to a drop in the pressure in the secondary chamber more rapid than can be offset by the induction of air from the atmosphere through therestricted orifice means comprising the compensating vent fitting 90. This means comprises essentially a pilot valve operable in response to such a drop in pressure in the chamber 139 and cavity 197 which, upon such operation, causes opening of a main valve admitting fluid under pressure to the split seat" of the dry pipe valve 10, i.e., the chamber designated by the reference numeral 53 in the U. S. Pat. of Rowley No. 2,667,934 previously referred to.

The pilot valve comprises a valve stem 200 slidably mounted in an opening 202 in a member 204 threaded into an opening 206 in one end of the member 132 and sealed thereto by a gasket, as shown; the valve stem 200 being sealed within the opening 202 by an O-ring as shown. At one end the valve stem 200 is provided with a valve head 208 which, in the closed position of the pilot valve, engages a seat 210 retained within the opening 206 in the member 132. At its opposite end the valve stem 200 is secured to a disk 212 which is adhesively secured to a diaphragm 214 the edge of which is retained between members and 204 by bolts 216 securing said members together. The opposite side of the diaphragm 214 is engaged by a disk 216 which is urged by a spring 218 compressed between the disk 216 and a wall of the member 195, in a direction to maintain the valve 208 in contact with its seat 210. The member 204 defines a cavity 220 which is in communication with the atmosphere through an opening 222, so that upon a drop in pressure in the primary chamber 139 and cavity 197 more rapid than can be offset by the induction of air from the atmosphere through the compensating vent fitting 90, the diaphragm 214 will move downwardly, as shown in FIG. 4, against the force of the spring 218, carrying the disk 212 adhesively secured thereto with it and removing the valve head 208 from its seat 210.

The main valve comprises a piston 224 slidably mounted in a valve chamber 226 in the member 132 and sealed to the walls thereof by an O-ring, as shown. Piston 224 is provided with a valve head 228 normally retained against a seat 230 by a spring 232 compressed between one end of a recess in the piston 224 and a plate 234 bolted and gasketed to the outside wall of the member 132; the piston 224, when so positioned, dividing the valve chamber 226 into two portions.

Fluid under pressure is constantly supplied to one portion of the cavity 226 from a source of fluid pressure which may be the air under pressure in the network of sprinkler piping of the automatic sprinkler system; the water under pressure in the main supply line 12; or an independent source of fluid pressure, through pipe 236 and port 238 (see also FIG. 5) in a wall of the cavity 226, also filling the other portion of cavity 226 by virtue of a constricted port 240 in the piston 224. The fluid under pressure also passes from 7 member 132 at the inlet side of the pilot valve 208.

Because the port 240 in the piston 224 is more constricted than the port 242 and the opening disclosed by the opening of the pilot valve 208 to the outlet side of the main valve, the 'opening of the pilot valve 208 creates a pressure differential across the piston 224, moving it leftward, as shown inFIG. 4, against the force of the spring 232, and removing the main valve 228 from its seat 230,This permits fluid under pressure to pass from the cavity 226 into a pipe 244 threaded into an opening 246 in the member 132 communicating with the outlet side of the main valve 228 and thence to i the split seat" of the dry-pipe valve 10, causing immediate opening thereof. I

In the operation of this embodiment of the device of the present invention, slow changes in the air pressure in the sprinkler piping network of the automatic sprinkler system are offset by the induction or expulsion of air from the chamber 139 and cavity 197 through the compensating vent fitting 90 without displacing the pilot valve 208 from its seat 210. However, inthe event of a rapid drop of air pressure in the sprinkler piping network,'such as the pressure drop produced by the opening of a thermally responsive valve of a sprinkler head, the pressure in the chamber 139 and cavity 197 drops more rapidly than air can be inducted through the compensating ve'nt fitting 90, thus producing a parfrom the supply pipe 236 through the main valve 228.

and thence through the pipe 244 to the pipe 22. The drain clapper valve 24 closes automatically, as described in the US. Pat. of Rowley No. 2,667,934, and the fluid pressure thereby created in the pipe 22 enters the split seat chamber designated 53 in said patent, causing immediate opening of the dry-pipe valve 10.

I claim:

1. A device of the character described comprising a compartment having piston means therein dividing the same into primary and secondary chambers, yieldable means-for impelling said piston means in a direction to decrease the volume of the secondary chamber and increase the volume of the primary chamber, a restricted orifice connecting said primary chamber with the atmosphere, a control device, means responsive to a decrease in pressure in said primary chamber by a predetermined amount below atmospheric pressure for actuating said control device, and means for introducing fluid under pressure into said secondary chamber to inhibit operation of said control device operating means. 7 e 

1. A device of the character described comprising a compartment having piston means therein dividing the same into primary and secondary chambers, yieldable means for impelling said piston means in a direction to decrease the volume of the secondary chamber and increase the volume of the primary chamber, a restricted orifice connecting said primary chamber with the atmosphere, a control device, means responsive to a decrease in pressure in said primary chamber by a predetermined amount below atmospheric pressure for actuating said control device, and means for introducing fluid under pressure into said secondary chamber to inhibit operation of said control device operating means. 